Inconclusive Polygraph Results: APA Standards & Best Practices

Defining the Inconclusive Outcome

A polygraph examination produces one of three possible diagnostic opinions: Deception Indicated (DI), No Deception Indicated (NDI), or Inconclusive (INC) [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. During the examination, physiological responses to relevant and comparison questions are measured across multiple channels — respiration, electrodermal activity (EDA), and cardiovascular activity — and each comparison spot is numerically scored. These values are summed to produce a total score. If the total score falls within the DI or NDI cutoff ranges established by the validated technique, the corresponding opinion is rendered.

However, when the total score falls in the numerical zone between DI and NDI thresholds — sometimes called the "inconclusive band" — the examiner cannot assign a definitive opinion. The width of this inconclusive band varies by technique. As Matte (2013) demonstrated, higher scoring thresholds increase accuracy while maintaining manageable inconclusive rates, with +3 and +1 score thresholds demonstrating equivalent 0.0 error rates [6]Verified The Connection between Score Threshold, Rate of Inconclusives and Minimum Number of Charts Required for Decision of Truth or Deception
Demonstrates that higher scoring thresholds increase accuracy while maintaining manageable inconclusive rates, with +3 and +1 thresholds showing equivalent 0.0 error rates.. These are standardized cutoffs considered the industry standard, though thresholds can be adjusted based on specific organizational requirements. For a deeper exploration of how numerical scoring systems work, see our guide to polygraph numerical scoring explained.

Incidence Rates in Professional Practice

The APA's meta-analytic survey of criterion accuracy provides the most authoritative data on inconclusive rates. This landmark 2011 meta-analysis reviewed 38 studies involving 3,723 examinations and 295 scorers [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers.. Event-specific (single-issue) diagnostic testing produced an aggregated decision accuracy of 89% with an estimated inconclusive rate of 11% [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers.. Multi-issue techniques produced an aggregated decision accuracy of 85% with an inconclusive rate of 13% [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers.. The combination of all validated PDD techniques, excluding outlier results, produced a decision accuracy of 87% with an inconclusive rate of 13% [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers..

The Empirical Scoring System (ESS) achieved a bootstrap mean accuracy rate of 87.9% with an inconclusive rate of 13.2% in replication studies, and notably, inexperienced examiners demonstrated comparable decision accuracy when using the ESS [3]Verified A Replication and Validation Study on an Empirically Based Manual Scoring System
Confirms ESS achieved bootstrap mean accuracy rate of 87.9% with inconclusive rate of 13.2%, and that inexperienced examiners demonstrated comparable decision accuracy using ESS.. Unlike binary classification systems that force every result into one of two categories, the three-category system acknowledges that measurement uncertainty is inherent in any psychophysiological assessment. Research by Saxe and Ben-Shakhar (1999) applied behavioral science concepts of reliability and validity to polygraph admissibility, arguing that accuracy rates are fundamentally probabilistic and called for mutual understanding between scientists and courts [10]Verified Admissibility of Polygraph Tests: The Application of Scientific Standards Post-Daubert
Applied behavioral science concepts of reliability and validity to polygraph admissibility, arguing accuracy rates are probabilistic..

Physiological and Medical Factors

Numerous physiological conditions can contribute to inconclusive results. Elevated general nervous tension, while expected and accounted for in properly conducted examinations, can sometimes produce ambiguous data patterns. Medical conditions such as respiratory issues, cardiovascular irregularities, and autonomic nervous system disorders may affect the quality of recorded data. Certain medications can also affect polygraph test results, including beta-blockers, anti-anxiety medications, and other substances that alter autonomic nervous system function.

Pain, fatigue, acute illness, and sleep deprivation are additional factors that can compromise data quality. The APA Standards of Practice require examiners to make reasonable efforts to determine that the examinee is a suitable candidate for polygraph testing, including basic inquiries into the medical and psychological condition of the examinee [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. Understanding the 9 factors that can affect lie detector test results is essential for both examiners and examinees.

Examiner-Related Causes

Research by Amsel (2016) demonstrated that the examiner's approach significantly impacts polygraph results [12]Verified Examiner Approach and its Impact on Polygraph Results
Demonstrates that interrogative examiner approaches compromise polygraph validity and can lead to false positives, as shown by the Jeffrey Deskovic wrongful conviction case.. Interrogative approaches aimed at extracting confessions rather than performing diagnostic truth assessment can compromise polygraph validity, increase examinee anxiety, and lead to ambiguous data patterns. The Jeffrey Deskovic wrongful conviction case powerfully illustrates this danger — the examiner used discredited methods and an excessively long, aggressive interrogation to elicit a false confession, conduct later described by expert witnesses as "professionally and scientifically outrageous" [12]Verified Examiner Approach and its Impact on Polygraph Results
Demonstrates that interrogative examiner approaches compromise polygraph validity and can lead to false positives, as shown by the Jeffrey Deskovic wrongful conviction case..

Poor question construction, inadequate pre-test interviews, failure to establish psychological set, and rushing through the examination process can all contribute to inconclusive outcomes. The APA mandates that examinations be scheduled for not less than 90 minutes [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards., and examiners must use evidence-based validated testing techniques [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For insights into how expert judgment complements objective scoring, see our article on polygraph examiner intuition in modern testing.

Environmental and Procedural Factors

Environmental conditions play a significant role in data quality. Excessive noise, uncomfortable temperatures, interruptions, and poor lighting can all affect an examinee's physiological responses. The testing environment should be controlled to minimize external stimuli that could contaminate the physiological data.

Procedural violations represent another significant cause. Failure to use a validated technique, improper sensor placement, insufficient number of chart presentations, and deviation from standardized question formats can all produce ambiguous data. The APA Standards require that questions used in the assessment of truth and deception be followed by time intervals of not less than 20 seconds from question onset to question onset [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. Additionally, the ASTM E2062 standard provides a comprehensive guide for PDD examination practice that helps examiners avoid procedural errors — learn more in our ASTM E2062 standards guide.

Countermeasures and Deliberate Distortions

Attempted countermeasures — deliberate physical or mental activities designed to manipulate physiological responses — can produce inconclusive results when the manipulated data prevents clean scoring. Shurany's (2015) Polygraph Validation Test (PVT) was specifically designed to address this problem and was successfully employed across 51 re-examinations of conflicted polygraph results, confirming suspected deliberate distortions through classic physiological patterns [13]Verified Using the Polygraph Validation Test (PVT) in Solving Conflicted Polygraph Results and Confirming Deliberate Distortions by Examinees
The PVT was successfully employed across all 51 re-examinations of conflicted polygraph results, confirming suspected deliberate distortions through classic physiological patterns..

The OSS-3 computerized scoring system, developed by Nelson, Krapohl, and Handler, includes statistical tests — specifically the Test of Proportions — to detect non-random artifacts in the data that may indicate strategic manipulation [4]Verified OSS-3 Objective Scoring System – Version 3
Confirms OSS-3 is a validated computerized scoring algorithm with demonstrable validity across multiple validation samples, providing balanced sensitivity and specificity.. When the statistical probability that the artifact pattern is random exceeds an alpha threshold, the data can be classified as statistically significant for non-random artifacts. This kind of advanced detection capability is one reason computerized scoring has become essential in modern polygraph practice, as detailed in our article on how software changed the lie detector test.

Standardized Diagnostic Terminology

The APA Standards of Practice (amended August 23, 2024) mandate the use of standardized reporting terminology [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For diagnostic examinations, results are reported as Deception Indicated (DI), No Deception Indicated (NDI), Inconclusive (INC), or No Opinion (NO) [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For screening examinations, the terminology shifts to Significant Response (SR), No Significant Response (NSR), Inconclusive (INC), or No Opinion (NO) [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For recognition tests, the terms are Recognition Indicated (RI), No Recognition Indicated (NRI), or No Opinion (NO) [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards..

The APA Model Policy for Paired Testing further clarifies that examiners shall report as Inconclusive (INC) or No Opinion (NO) when sufficient criteria do not exist to render an opinion [5]Verified APA Model Policy for Paired Testing
Confirms that examiners shall report as Inconclusive (INC) or No Opinion (NO) when sufficient criteria do not exist to render an opinion.. This standardized vocabulary ensures consistency across the profession and prevents confusion when results are communicated to requesting agencies, attorneys, courts, or treatment providers. For more on paired testing protocols, see our guide to paired testing examinations.

Maximum Acceptable Inconclusive Rates

The APA sets clear boundaries for acceptable inconclusive rates in validated techniques. For evidentiary examinations, polygraph techniques must demonstrate an unweighted average accuracy rate of 90% or greater, excluding inconclusive results, which shall not exceed 20% [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For investigative testing, techniques must demonstrate an unweighted average accuracy rate of 80% or greater, with inconclusive results not exceeding 20% [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards..

The three-position scoring model was excluded from the APA meta-analysis specifically because its inconclusive rates consistently exceeded this 20% boundary [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers.. However, the meta-analysis noted that three-position accuracy did not differ significantly from seven-position accuracy, so field practices using three-position scoring as an initial analysis may be acceptable if inconclusive results are subsequently resolved using a method that meets APA requirements [2]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 11% inconclusive rate for single-issue tests, 13% for multi-issue, 87% overall decision accuracy, 38 studies involving 3,723 examinations and 295 scorers.. This is an important nuance in understanding how different scoring approaches — detailed in our Bayesian vs. frequentist statistics guide — affect overall inconclusive rates.

Documentation Requirements

APA Standards require thorough documentation of all examination phases. Examiners must maintain all polygraph reports, test questions, data, recordings, information, and documents related to the pre-test, in-test, and post-test phases for a minimum of three years or as otherwise required by law [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. An audio or audio-video recording of all phases of the exam must be maintained for a minimum of one year [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards..

A test result shall not be considered final until it is documented in the examination report and issued to the referring professional or agency [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. Where examinations deviate from the protocols of a validated polygraph technique, the deviations must be explained in writing [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. For inconclusive results specifically, this documentation should include the probable cause of the inconclusive outcome, any observed physiological anomalies, environmental factors, and recommendations for follow-up testing.

Why the Three-Category System Exists

The three-category system (DI, NDI, INC) represents a fundamental commitment to scientific honesty in polygraph testing. Unlike binary systems that force every result into a definitive classification, the three-category approach acknowledges that measurement uncertainty is an inherent feature of any psychophysiological assessment. This approach actually strengthens the credibility of definitive results — when an examiner reports DI or NDI, the profession's willingness to acknowledge uncertainty through the INC category means those definitive opinions carry greater weight.

Research by Widacki (2014) examined the evidentiary status of polygraph results, concluding that they are classified as circumstantial evidence requiring logical inference rather than direct evidence [11]Verified Results of Polygraph Examinations: Direct or Circumstantial Evidence?
Polygraph results are classified as circumstantial evidence requiring logical inference rather than direct evidence.. This classification reinforces the importance of the three-category system — examiners must report what the data actually supports rather than over-interpreting ambiguous results. Understanding the role of prior probabilities in polygraph testing helps put these classifications into proper statistical context.

The Problem with Treating Inconclusive as Deception

Honts (2021) conducted a comprehensive meta-analysis of 138 datasets on comparison question polygraph tests and documented a concerning practice among some agencies: treating inconclusive outcomes as indications of deception [9]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Comprehensive meta-analysis of 138 datasets on comparison question polygraph tests documenting accuracy and some concerning agency practices regarding inconclusive outcomes.. The meta-analysis revealed that certain federal agencies deliberately chose specific CQT variants, scoring systems, and decision rules to minimize false negative errors with almost no concern for false positive errors, including policies of treating inconclusive outcomes as deceptive [9]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Comprehensive meta-analysis of 138 datasets on comparison question polygraph tests documenting accuracy and some concerning agency practices regarding inconclusive outcomes..

This practice directly violates the scientific basis of polygraph testing and the APA's standards. The APA FAQ page specifically states that those who use polygraph testing do not consider inconclusive test results as meaningful and do not hold them against the examinee [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs.. In a real-life setting, an inconclusive result simply means the examiner is unable to render a definite diagnosis of truth or deception, and in such cases a second examination is usually conducted at a later date [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs.. For more on minimizing false positives and negatives in polygraph testing, see our dedicated guide.

Advanced Scoring Techniques: Weighted EDA and Multinomial Cut-Scores

The most significant research breakthrough in reducing inconclusive results comes from Nelson and Handler's (2018) descriptive analysis of decision rules, weighted electrodermal scores, and multinomial cut-scores [8]Verified Reducing Inconclusive Results: A Descriptive Analysis of Decision Rules, Weighted Electrodermal Scores and Multinomial Cut-Scores
Weighted EDA scores alone reduced inconclusive results by 49%, while combining EDA weighting with multinomial cut-scores achieved a 72% reduction in inconclusive outcomes.. Their study demonstrated that weighted EDA scores alone produced an average 49% reduction of inconclusive results, while combining EDA weighting with multinomial cut-scores achieved a remarkable 72% reduction in inconclusive outcomes [8]Verified Reducing Inconclusive Results: A Descriptive Analysis of Decision Rules, Weighted Electrodermal Scores and Multinomial Cut-Scores
Weighted EDA scores alone reduced inconclusive results by 49%, while combining EDA weighting with multinomial cut-scores achieved a 72% reduction in inconclusive outcomes..

This research builds on the well-established finding that electrodermal activity (EDA) is the most diagnostic physiological channel in polygraph testing. EDA accounted for approximately 54% of the diagnostic variance in sample data, while cardiovascular activity accounted for 34% and respiration for 12% [8]Verified Reducing Inconclusive Results: A Descriptive Analysis of Decision Rules, Weighted Electrodermal Scores and Multinomial Cut-Scores
Weighted EDA scores alone reduced inconclusive results by 49%, while combining EDA weighting with multinomial cut-scores achieved a 72% reduction in inconclusive outcomes.. The ESS scoring system implements this weighting by allowing EDA scores to have integer values of [-2, 0, +2] while other sensor scores are limited to [-1, 0, +1], effectively giving EDA data double the diagnostic weight in the final score calculation.

Different decision rules — including federal-zone-rules, grand-total-rule, subtotal-score-rule, and two-stage-rules — had less effect when combined with multinomial cut-scores than with traditional cut-scores [8]Verified Reducing Inconclusive Results: A Descriptive Analysis of Decision Rules, Weighted Electrodermal Scores and Multinomial Cut-Scores
Weighted EDA scores alone reduced inconclusive results by 49%, while combining EDA weighting with multinomial cut-scores achieved a 72% reduction in inconclusive outcomes.. This finding suggests that the combination of weighted EDA and multinomial reference distributions provides a robust reduction in inconclusive rates regardless of the specific decision rule employed.

Computerized Scoring Algorithms

The OSS-3 (Objective Scoring System, version 3), developed by Raymond Nelson, Donald Krapohl, and Mark Handler, is a validated computerized scoring algorithm with demonstrable validity across multiple validation samples [4]Verified OSS-3 Objective Scoring System – Version 3
Confirms OSS-3 is a validated computerized scoring algorithm with demonstrable validity across multiple validation samples, providing balanced sensitivity and specificity.. Because the OSS-3 derives scores from measurements of the Kircher features using ratio transformations, it eliminates subjectivity in chart interpretation and provides perfect inter-rater reliability [4]Verified OSS-3 Objective Scoring System – Version 3
Confirms OSS-3 is a validated computerized scoring algorithm with demonstrable validity across multiple validation samples, providing balanced sensitivity and specificity..

The ESS (Empirical Scoring System) represents another major advancement. In validation studies, inexperienced examiners using the ESS achieved an average decision accuracy of 88% with only 13.1% inconclusives, and their sensitivity and specificity levels did not differ significantly from experienced scorers [3]Verified A Replication and Validation Study on an Empirically Based Manual Scoring System
Confirms ESS achieved bootstrap mean accuracy rate of 87.9% with inconclusive rate of 13.2%, and that inexperienced examiners demonstrated comparable decision accuracy using ESS.. Both algorithms are bundled with Lafayette Instrument's LXSoftware polygraph platform [14]Verified LXSoftware — Lafayette Instrument Company
Confirms OSS-3 and ESS scoring algorithms are bundled with Lafayette Instrument's LXSoftware polygraph platform., making advanced scoring capabilities accessible to all practitioners.

Best practices research by Dutton (2020) used Monte Carlo simulations based on 299 subtotal scores to provide the first systematic criterion accuracy estimates and confidence intervals for two-relevant-question multi-issue examinations, confirming that each question must be evaluated independently [15]Verified Best Practices in Polygraph Examination
Monte Carlo simulations based on 299 subtotal scores provided systematic criterion accuracy estimates for two-relevant-question multi-issue examinations.. This work further refines the tools available for reducing inconclusive rates in screening contexts.

Optimal Examination Procedures

Beyond scoring innovations, proper examination procedures significantly reduce inconclusive rates. The APA mandates a minimum examination duration of 90 minutes [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. However, many examinations — particularly in security clearance contexts — take considerably longer. The NSA advises that the average test length for security polygraphs falls between 2 to 4 hours [17]Verified NSA Polygraph Examination Information
Confirms that the average NSA polygraph test length falls between 2-4 hours..

Adequate time allocation enables thorough pre-test interviews, proper physiological data collection, and the collection of sufficient chart presentations. Examiners should conduct an acquaintance test for all diagnostic, evidentiary, paired-testing, initial screening, and initial investigative examinations [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. Questions should be carefully constructed to be clear, unambiguous, and answerable with a yes or no response. For guidance on question construction principles, see our article on norming questions in polygraph testing.

The role of salience in polygraph testing — particularly how the psychological weight of relevant questions influences physiological responses — is a critical factor in reducing inconclusive outcomes. When comparison questions are properly calibrated in salience relative to relevant questions, clearer differential responses emerge.

Continuing Education and Quality Control

Ongoing examiner education is essential for maintaining low inconclusive rates. The APA requires that examiners attend continuing education to stay current with the latest research, techniques, and best practices [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. The basic polygraph examiner course consists of a minimum of 400 hours of instruction, and specialized training — such as PCSOT certification — adds additional competency requirements.

Quality control review of examination files helps identify patterns that may contribute to elevated inconclusive rates. Blind scoring of chart data by independent reviewers, calibration exercises among examiners, and regular comparison of individual examiner metrics against published norms all contribute to improved outcomes. For networking opportunities and professional development, see our guide to polygraph examiner conferences and events in 2025.

When and How to Retest

The APA FAQ confirms that when an inconclusive result occurs, a second examination is usually conducted at a later date [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs.. The key is identifying the probable cause of the inconclusive result and making targeted adjustments for the subsequent examination.

Follow-up testing considerations include: allowing a sufficient waiting period to reduce accumulated stress, potentially modifying test questions to improve clarity, addressing any identified medical or environmental factors, and potentially using a different examiner if examiner rapport was a contributing issue. The waiting period should balance the need for timely results against the need for the examinee's physiological state to normalize.

For techniques used in follow-up testing, the Federal Zone Comparison Technique and Zone Comparison Test (ZCT) offer well-validated frameworks with established decision rules that can be adjusted for follow-up contexts.

Using the Polygraph Validation Test (PVT) for Conflicted Results

Shurany's (2015) Polygraph Validation Test (PVT) provides a specialized tool for resolving conflicted polygraph results, including cases where countermeasures or deliberate distortions may have contributed to an inconclusive outcome [13]Verified Using the Polygraph Validation Test (PVT) in Solving Conflicted Polygraph Results and Confirming Deliberate Distortions by Examinees
The PVT was successfully employed across all 51 re-examinations of conflicted polygraph results, confirming suspected deliberate distortions through classic physiological patterns.. The PVT was successfully employed across all 51 re-examinations of conflicted polygraph results in the study, confirming suspected deliberate distortions through classic physiological patterns known as POT (Peak of Tension) reactions [13]Verified Using the Polygraph Validation Test (PVT) in Solving Conflicted Polygraph Results and Confirming Deliberate Distortions by Examinees
The PVT was successfully employed across all 51 re-examinations of conflicted polygraph results, confirming suspected deliberate distortions through classic physiological patterns..

The PVT works by presenting the examinee with a structured series of stimuli designed to reveal whether they have improperly focused attention on comparison questions or employed other manipulation strategies. When POT reactions indicate deliberate distortion, the examiner has a documented, scientifically defensible basis for their findings. This tool is particularly valuable in high-stakes contexts where the integrity of the examination process is paramount — see our guide to high-stakes polygraph examinations for more information.

Professional Conduct Standards

The APA requires examiners to maintain a professional, objective, diagnostic approach throughout the examination. The examiner's role is to perform a valid psychophysiological assessment — not to extract confessions or advocate for a particular outcome. As Amsel (2016) powerfully demonstrated, when examiners adopt an interrogative rather than diagnostic approach, the validity of the entire examination is compromised [12]Verified Examiner Approach and its Impact on Polygraph Results
Demonstrates that interrogative examiner approaches compromise polygraph validity and can lead to false positives, as shown by the Jeffrey Deskovic wrongful conviction case..

Examiners must never speculate beyond what the data supports. An inconclusive result means exactly what it says — the data is insufficient to support a definitive opinion. Examiners should provide honest, standardized explanations to all parties, including the examinee, the requesting agency, and any legal representatives. The profession's credibility depends on this commitment to scientific integrity.

Konieczny's (2007) case study exploring the relationship between false memory techniques and polygraph test validity further underscores the importance of examiner vigilance against all potential threats to examination integrity [16]Verified An Attempt to Falsify the Results of a Polygraph Test Through the Implementation of False Memory: A Case Study
Explored the relationship between false memory techniques and polygraph test validity..

Communication with Stakeholders

Effective communication of inconclusive results requires sensitivity and precision. Examinees should be told clearly that an inconclusive result is not a finding of deception and carries no implication of guilt. Requesting agencies should receive a detailed written report explaining the inconclusive finding, the probable contributing factors, and recommendations for follow-up.

In legal contexts, attorneys should understand that polygraph results are classified as circumstantial evidence [11]Verified Results of Polygraph Examinations: Direct or Circumstantial Evidence?
Polygraph results are classified as circumstantial evidence requiring logical inference rather than direct evidence. and that an inconclusive finding has no evidentiary value regarding the examinee's veracity. In PCSOT contexts, the containment team — including treatment providers, probation officers, and the polygraph examiner — should collaborate to determine the best course of action following an inconclusive result. PCSOT is utilized in 79% of adult and 50% of adolescent community sex offender treatment programs across the US [18]Verified Current Practices and Emerging Trends in Sexual Abuser Management: The Safer Society 2009 North American Survey
Documents PCSOT utilized in 79% of adult and 50% of adolescent community sex offender treatment programs across the US, up from 29% in 1992., making proper handling of inconclusive results in this context especially important.

Security Clearance Polygraph Examinations

For security clearance polygraph examinations, inconclusive results carry particular significance. According to SEAD-4 (Security Executive Agent Directive 4), signed by the Director of National Intelligence and effective June 8, 2017, the National Security Adjudicative Guidelines state that "no adverse action concerning these guidelines may be taken solely on the basis of polygraph examination technical calls in the absence of adjudicatively significant information" [19]Verified SEAD-4: National Security Adjudicative Guidelines
Confirms that no adverse action may be taken solely on the basis of polygraph examination technical calls in the absence of adjudicatively significant information.. This protection applies to all covered individuals who require initial or continued eligibility for access to classified information or eligibility to hold a sensitive position.

However, it is important to note that while a security clearance cannot be denied solely on the basis of a polygraph result, agencies may use polygraph results in conjunction with other investigative findings [19]Verified SEAD-4: National Security Adjudicative Guidelines
Confirms that no adverse action may be taken solely on the basis of polygraph examination technical calls in the absence of adjudicatively significant information.. Additionally, there is no national policy that prevents an agency from rejecting an applicant based on employment suitability criteria if the applicant does not successfully complete a polygraph exam. The NSA polygraph process, for example, involves sessions that typically last between 2 to 4 hours [17]Verified NSA Polygraph Examination Information
Confirms that the average NSA polygraph test length falls between 2-4 hours., and applicants may be called back for multiple sessions before a final determination is made.

Law Enforcement and Criminal Investigation

In law enforcement contexts, inconclusive results present specific operational challenges. The APA reports that 62% of the largest police agencies in the United States have active polygraph screening programs [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs.. When pre-employment screening produces an inconclusive result, many agencies will schedule a retest after an appropriate waiting period.

In criminal investigation contexts, an inconclusive result means the polygraph has not provided the investigative lead that was sought. The examination should not be characterized as a "failed" test, and the inconclusive finding should not be used to support investigative conclusions. Honts's (2021) meta-analysis documented that some agency practices regarding inconclusive outcomes — particularly treating them as deceptive — are not scientifically supported and can lead to unjust outcomes [9]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Comprehensive meta-analysis of 138 datasets on comparison question polygraph tests documenting accuracy and some concerning agency practices regarding inconclusive outcomes.. For information on how polygraph testing functions in law enforcement hiring, see our guide to polygraph tests in Florida police hiring.

PCSOT and Sex Offender Supervision

Post-Conviction Sex Offender Testing (PCSOT) presents unique considerations for inconclusive results. The APA's Model Policy for PCSOT emphasizes that polygraph examiners should consider themselves an integral part of the multidisciplinary supervision and treatment team. The primary goal of PCSOT is to increase public safety by adding incremental validity to risk assessment and treatment planning decisions.

When a PCSOT examination produces an inconclusive result, the containment team — comprising the probation officer, treatment provider, and polygraph examiner — should collaborate to determine appropriate next steps. An inconclusive result should not automatically trigger sanctions but should prompt further investigation and potentially a follow-up examination. The 2009 Safer Society North American Survey documented that PCSOT was utilized in 79% of adult and 50% of adolescent community sex offender treatment programs, up from 29% in 1992 [18]Verified Current Practices and Emerging Trends in Sexual Abuser Management: The Safer Society 2009 North American Survey
Documents PCSOT utilized in 79% of adult and 50% of adolescent community sex offender treatment programs across the US, up from 29% in 1992., reflecting the profession's growing confidence in polygraph as a supervision tool. Learn more about the therapeutic alliance in our guide to PCSOT and treatment providers.

Private Sector and EPPA Considerations

In the private sector, the Employee Polygraph Protection Act (EPPA) of 1988 prohibits most private employers from using polygraph testing to screen applicants for employment [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs.. However, testing of employees is permitted to solve an employer's "economic loss," and there are exemptions for guards, armored car personnel, and those who handle drugs and narcotics [7]Verified Polygraph Frequently Asked Questions
Confirms that inconclusive results are not considered meaningful or held against examinees, that second examinations are usually conducted, and provides data on 62% of largest police agencies having active polygraph screening programs..

Under EPPA, examiners must administer no test that is less than 90 minutes in duration [1]Verified APA Standards of Practice (Amended 8-23-24)
Confirms standardized reporting terminology (DI, NDI, INC, NO), 90-minute minimum exam duration, 20% maximum inconclusive rate for validated techniques, documentation requirements, and examiner conduct standards.. When an inconclusive result occurs in an EPPA-covered examination, the employer may not take adverse action against the employee based on that result. The examiner must maintain detailed records of the examination and its results for a minimum of three years. For specific applications, see our guides on jewelry store theft polygraph and Delaware private polygraph testing.

Historical Context and 100 Years of Progress

Slowik (2020) documented the most important changes in polygraphy over its 100-year evolution, tracing the field's development from the 1930 Northwestern crime laboratory through subsequent field research by John Reid and Fred Inbau that transformed polygraphy from rudimentary physiological measurements into a structured scientific discipline [20]Verified Critical Changes Over the 100 Year Evolution of Polygraph Practices
Documents the most important changes in polygraphy originating from the 1930 Northwestern crime laboratory and subsequent field research.. The refinement of scoring methodologies over this century has directly contributed to reduced inconclusive rates.

The progression from subjective global analysis to numerical scoring systems, and from manual scoring to computerized algorithms, represents a continuous effort to reduce measurement uncertainty and improve diagnostic accuracy. Each advancement — the comparison question technique in 1947, numerical scoring systems, the OSS-3 algorithm in 2008, the ESS in 2011, and multinomial reference distributions — has contributed to more precise diagnostic boundaries and consequently more manageable inconclusive rates.

Future Directions in Reducing Inconclusive Results

The development of deep-learning-based computerized scoring algorithms represents the next frontier in reducing inconclusive rates. Recent research has used PolyScore and OSS-3 as established benchmarks for comparing new deep-learning approaches [21]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm
Confirms PolyScore and OSS-3 as established computerized scoring algorithms used as benchmarks for comparing new deep-learning-based scoring systems.. These machine learning methods hold promise for extracting additional diagnostic information from physiological data that current scoring models may not capture.

Bayesian analysis methods, as implemented in the ESS multinomial reference model, represent another promising direction. By providing simpler and more intuitive discussion about the likelihood of deception or truth-telling compared to traditional frequentist approaches, Bayesian methods may help examiners make more confident diagnostic decisions while maintaining scientific rigor. For a thorough comparison of these statistical approaches, see our article on Bayesian vs. frequentist statistics in polygraph testing.